THE FUNGI 



183 



forms this shows a central more compact body surrounded by a 

 weft of looser filaments, which completely invests the young fruit. 

 In Coprinus the young fruit soon shows the expanded cap (Pileus) 

 at the top of the short, thick stalk. The cap, which is flat at first, 

 grows downward over the stalk, which it completely covers. As 

 the cap develops, there are formed upon its inner surface the radiat- 

 ing lamellse or Gills, upon which later the hymenimn is formed. A 

 section of the gill shows that the inner tissue (Trama) is composed 

 of large, rather loose hyphse, much like those forming the body of 

 the fruit. The ends of these hyphse are turned outward and form 

 a layer of papillate cells covering the whole of the surface of the 

 gill. This superficial layer is the hymenium, and some of its cells 

 become later transformed into the basidia, while others remain 

 sterile. Some of these sterile cells may become very much enlarged 

 and form the " Cystidia." 



-g 



FIG. 148. Mushroom (Psalliota campestris). A, mycelium with fruit-bodies in 

 various stages of development. B-D, sections of young fruit-bodies, showing the 

 development of the gills, g. (All after ATKINSON.) 



The basidia in Coprinus are club-shaped bodies tapering below 

 and somewhat flattened at the top, from which grow the sterigmata, 

 which are usually four in number, but may be reduced to two or 

 three (Fig. 147, E, F). 



Development of Spores. The development of the basidia and spores has been 

 specially studied by Wager (26). In the young basidium there are two or more 

 nuclei. These fuse into a single one, which later divides into four, correspond- 

 ing to the four spores. The sterigmata begin to form after this division is com- 

 plete, and most of the granular contents of the basidium pass into the spores, 

 which reach their full size, and sometimes develop the brown wall, before the 

 nuclei pass over from the basidium. The way in which the nuclei pass through 

 the narrow sterigma into the spore has not been clearly demonstrated. After 

 entering the spore, the nucleus divides into two. 



